This invention is generally in the field of devices and methods for the transdermal drug delivery and analyte sensing.
Transdermal drug delivery systems generally rely on diffusion of drug across the skin. In a typical conventional technology, the transdermal drug delivery system is in the form of a multi-layered patch that includes a backing or cover layer, a drug matrix/reservoir, a diffusion control membrane, and an adhesive layer for attaching the system to the surface of the skin. Examples of drugs delivered with such systems include scopolamine (Trasderm-Scop™), nicotine, nitroglycerin (Nitro-Dur™), estradiol (Estraderm™), and testosterone. However, transdermal patches generally are unsuitable for delivery of macromolecules. Others have sought to improve transdermal delivery of drug molecules, particularly where the size and hydrophilicity of the drug molecules significantly hinders diffusion through the stratum corneum, over that obtained with passive diffusion alone, by including with the transdermal drug delivery systems an active mechanism, such as iontophoresis, electroporation, ultrasound, or heat, or by disrupting the stratum corneum with microneedles or the like.
In transdermal and other drug delivery systems, it is generally desirable to store and protect the drug formulation until the time it is to be delivered to a patient, because exposure to environmental components (e.g., oxygen, humidity) may damage or prematurely degrade the pharmaceutical agent. However, in various conventional transdermal drug delivery systems which contain several days worth of doses of the drug, the entire drug formulation is contained in a single reservoir, such that is it not possible to protect or isolate individual doses. It would be desirable to be able to do so, particularly for relatively fragile pharmaceutical agent molecules.
In addition, with a conventional patch-type drug delivery system, it generally is not possible to change or fine-tune the rate of administration of drug once the patch is applied to the patient. It would be desirable to provide new and improved methods and devices for the controlled delivery of one or more drugs to a patient by transdermal administration. For example, it would be advantageous to be able to store and transdermally administer multiple discrete doses of a drug formulation, using a device which the physician can easily vary or fine tune the time and rate of drug administration.